TypeError: unsupported operand type(s) for +: int and list

TypeError: unsupported operand type(s) for +: int and list #

The Python "TypeError: unsupported operand type(s) for +: 'int' and 'list'" occurs when we try to use the addition (+) operator with a number and a list. To solve the error, figure out where the variable got assigned a list and correct the assignment, or access a specific value in the list.

Here is an example of how the error occurs.

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my_int = 10
my_list = [20, 30, 40]

# ⛔️ TypeError: unsupported operand type(s) for +: 'int' and 'list'
result = my_int + my_list

We are trying to use the addition (+) operator with a list and a number.

If you need to iterate over the list and add a value to each number, use a list comprehension.

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my_int = 10
my_list = [20, 30, 40]

my_new_list = [x + my_int for x in my_list]
print(my_new_list)  # 👉️ [30, 40, 50]

The same can be achieved using a simple for loop.

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my_int = 10
my_list = [20, 30, 40]

my_new_list = []

for num in my_list:
    my_new_list.append(num + my_int)

print(my_new_list)  # 👉️ [30, 40, 50]

If you need to use the addition (+) operator on an item in the list, access the item at its specific index.

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my_int = 10
my_list = [20, 30, 40]

result = my_int + my_list[0]

print(result)  # 👉️ 30

We accessed the list item at index 0 and added 10 to it.

If you need to get the sum of the list, use the sum() function.

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my_int = 10
my_list = [20, 30, 40]

result = my_int + sum(my_list)

print(result)  # 👉️ 100

print(sum(my_list))  # 👉️ 90

The sum function takes an iterable, sums its items from left to right and returns the total.

The sum function takes the following 2 arguments:

You can pass the other number as the start value to the sum() function.

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my_int = 10
my_list = [20, 30, 40]

result = sum(my_list, my_int)

print(result)  # 👉️ 100

print(sum(my_list))  # 👉️ 90

If you aren't sure what type a variable stores, use the built-in type() class.

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my_int = 10
print(type(my_int))  # 👉️ <class 'int'>
print(isinstance(my_int, int))  # 👉️ True

my_list = [20, 30, 40]
print(type(my_list))  # 👉️ <class 'list'>
print(isinstance(my_list, list))  # 👉️ True

The type class returns the type of an object.

The isinstance function returns True if the passed in object is an instance or a subclass of the passed in class.

Conclusion #

The Python "TypeError: unsupported operand type(s) for +: 'int' and 'list'" occurs when we try to use the addition (+) operator with a number and a list. To solve the error, figure out where the variable got assigned a list and correct the assignment, or access a specific value in the list.